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Index ~~ Background ~~ Purpose ~~ Hypothesis ~~ Materials ~~ Earthquake Machine ~~ Modifications: Overlapping - Height - Buttresses - Base Isolators - Cross Braces - Roofs ~~ Resistant Buildings ~~ Problems ~~ Further Experimentation ~~ Bibliography |
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PAGE INDEX: How earthquakes damage buildings
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An earthquake is a sudden shaking of the ground caused by the movements beneath the earth's crust. The crust is made up of huge rocks called plates. The plates slowly rub against each other causing pressure to build up beneath the surface. When the pressure becomes too much the plates jolt past each other sending out the shockwaves that produce an earthquake (Morris, p.4).
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 The San Francisco 1906 earthquake |
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The shockwaves are called seismic waves. Some types of seismic waves are called body waves. There are two different types of body waves: primary and secondary. Primary waves are fast and move like a slinky and secondary waves move more slowly and only move through rock. They travel by moving up and down like an ocean wave. The other waves are called surface waves. There are two different types of surface waves: Rayleigh waves and Love waves. They move slower than the body waves and last five times longer. Love waves cause most of the damage in an earthquake (Walker, p.16).
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The 2003 earthquake in the ancient Iranian city of Bam measured 6.6 on the Richter scale and killed over 40 000 people. Even though the 1989 Loma Prieta earthquake measured 7.1 on the Richter scale, only 62 people lost their lives. California's dramatically lower death toll is in large part due to scientists increasing understanding of how buildings react to earthquakes and the new technologies they have developed to help structures withstand them (Schwartz, p.1).
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Structural engineers are trying to make earthquake resistant buildings using different methods. They aren’t just making buildings stronger, the structures have devices that absorb energy from earthquakes (Schwartz, p.1).
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It is possible to make a building that is strong yet protected from earthquakes because the base of the building sits on slick friction bearing pads. They reduce the spread of the movement of the ground to the building during an earthquake (Horton, p. 1). It will just rock back and forth like a boat (Schwartz, p. 2). The pads reduce the shaking by as much as 5 times in a large earthquake and 3 times in a smaller one (Horton, p. 1). |
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A tuned mass damper (TMD) helps spread out the energy of an earthquake.
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Besides base isolators, engineers can use damping systems to absorb seismic energy. Dampers stop the building from moving back and forth by moving in the opposite direction. An example of a damper is a water tank put in a building so when the earthquake shakes the building the water sloshes the other way. A more sophisticated damper is called a tune mass damper. In a tune mass damper, a mass or a weight vibrates in the opposite direction of the earthquake waves lessening the effect of the earthquake (Design, p. 1-2). |
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The structural system of a building needs to be flexible, capable of stretching and bending. It also helps if the building is constructed in a way that it vibrates as one unit and sways together.
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 High Technology Skyscrapers can use a lot of technology. Stabilizing devices work during an earthquake like giant car shock absorbers to slow the movement of floors. Some of these devices even turn the energy of the earthquakes' movement into heat (Schwartz, p. 1).
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 Low Technology Engineers can make buildings earthquake resistant in ways that involve very little technology. For example, houses in South America: the walls of the homes were made by tying wooden poles together in a pattern similar to the strings of a tennis racket (Walker, p. 42). The walls of this home in Columbia are built to crumble into small, harmless pieces during an earthquake.
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(a) Roofs A roof can help hold a building up. It helps tie the building together so it can act as one unit during an earthquake. (b) Buttresses Buttresses reinforce and stabilize the building and they also provide another pathway for the energy to dissipate (ArchNet, p. 2). Buttresses can be added to existing buildings to make them earthquake resistant.
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(c) Overlapping Overlapping construction has been used to improve the stability of buildings for thousands of years. For example, the Todaiji Temple built in Japan in 743 AD is the largest wooden building in the world. It has a log house construction with walls intersecting in the corners. It has stood through many earthquakes (web-japan, p. 2). |
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